1. Technical Field
The present invention relates to a battery charger, a voltage monitoring device and a self-diagnosis method of a reference voltage circuit.
2. Related Art
In recent years, a voltage adjusting device has been used in a battery for a vehicle or the like. For example, Japanese Patent Application Laid-Open (JP-A) No. 2009-38857 discloses a voltage adjusting device that measures a voltage of each of a plurality of battery cells connected in series to each other using a voltage detecting circuit and repeats a charging/discharging operation in accordance with variations in the entire battery cells.
On the other hand, JP-A No. 2003-319565 discloses a charging monitoring device including a voltage measuring unit that has an attenuator decreasing a voltage across terminals of a battery in accordance with a predetermined ratio, an A/D converter A/D converting the output voltage of the attenuator, and a reference voltage generating circuit supplying an A/D conversion reference voltage to the A/D converter, and a charging monitoring control section that executes and controls a process of monitoring a charging condition on the basis of information of the voltage measuring unit and the like.
According to the battery charging control device of JP-A No. 2003-319565, as a method of determining an abnormal operation of the voltage measuring unit, there is disclosed a method of determining that the voltage measuring unit is abnormal when a measurement value of the voltage measuring unit is not abnormal even when the charging condition of the battery is abnormal.
However, in the abnormality detecting method of the voltage measuring unit disclosed in JP-A No. 2003-319565, an abnormality of the voltage measuring unit cannot be detected when the charging condition of the battery is not clearly abnormal. For this reason, when the method is applied to, for example, a battery for a vehicle or the like, there is a concern in that an erroneous operation due to the abnormal charging condition, disconnection of a power supply line, ignition, or the like may be caused. Therefore, it is not desirable to adopt the method since the method is very dangerous from the viewpoint of maintaining safety.
Further, JP-A No. 8-56160 discloses a technique for checking an operation of the A/D converter in a manner such that a predetermined reference voltage obtained in a test mode is input to the A/D converter and conversion data is compared with the predetermined value to determine whether the two are equal to each other.
An object of the present invention is to provide a battery charger capable of detecting abnormality of an A/D converter and a reference voltage circuit, a voltage monitoring device and a self-diagnosis method of a reference voltage circuit.